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Mendel I Notes

Mendel I Notes. CP Biology Ms. Morrison. Genetics: scientific study of heredity. Gregor Mendel. Austrian monk – in mid 1800s taught high school and took care of the monastery gardens Garden stocked with true breeding pea plants True-breeding = always have identical offspring

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Mendel I Notes

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  1. Mendel I Notes CP Biology Ms. Morrison

  2. Genetics: scientific study of heredity

  3. Gregor Mendel • Austrian monk – in mid 1800s taught high school and took care of the monastery gardens • Garden stocked with true breeding pea plants • True-breeding = always have identical offspring • Ex. Tall plants always produce more tall plants • Controlled how plants pollinated • Did not allow self-pollination • Cross pollinated between different pea plants

  4. Mendel’s Pea Plant Experiments • Studied 7 pea plant traits • Trait = specific characteristic, ex. Plant height • Crossed two true-breeding pea plants • Starting plants = P (parental) generation, one tall and one short • All offspring = hybrids (offspring of parents with different traits) • Offspring generation = F1 (first filial) • Had expected blend of parents’ traits – thought plants would have medium height • Actual results – all plants tall, short trait disappeared

  5. Mendel’s Conclusions • First – biological inheritance is determined by factors passed from one generation to the next • Genes = chemical factors that determine traits • Genes have two contrasting forms (tall, short) • Alleles = different forms of a gene

  6. Mendel’s Conclusions • Second – principle of dominance: some alleles are dominant and some are recessive • Dominant allele always shows • Recessive allele only shows when not dominant allele present • Tall = dominant, short = recessive

  7. Mendel’s Further Experiments • Crossed F1 hybrid offspring to determine if recessive allele still present • Offspring = F2 generation • 75% tall • 25% short – recessive allele reappeared

  8. Mendel’s Final Conclusions • At some point recessive allele was separated from the dominant allele in F1 = segregation of alleles • Suggested that segregation of alleles occurred during formation of gametes – meiosis • Gametes only carry single copy of each gene • Offspring inherit one allele from each parent (so they have two alleles total)

  9. Probability • Is likelihood that an event will occur • Mendel realized outcomes of genetic crosses could be predicted using probability • Punnett square – diagram that shows the genetic combinations that might result from a genetic cross • Dominant alleles are capitals, ex. Tall, T • Recessive alleles are lowercase, ex. Short, t

  10. Genetics Terms • Homozygous (true-breeding): have two identical alleles, ex. TT or tt • Heterozygous (hybrid): have 2 different alleles, ex. Tt • Phenotype = physical appearance (what organism looks like) • Genotype = genetic makeup (organism’s actual alleles) • NOTE – can have same phenotype but different gentotype, ex. TT and Tt both look tall

  11. Punnett Square Example 1 • F1 results: • Phenotype: 100% tall • Genotype: 100% Tt

  12. Punnett Square Example 2 • F2 results: • Phenotype: (3:1) • 75% tall • 25% short • Genotype: (1:2:1) • 25% TT • 50% Tt • 25% tt

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